It would defintely be unusual to use one in a bass rig, in fact I can't say I've heard of it. I have a couple of them, for guitar into older, somewhat dark sounding, non master volume amps, so I can get some more highs and a bit more gain to get a nice vintage crunch. For bass, I tend to use amps that are more flexible in and of themselves in the preamp, and any distortion I would use would be in the amp and speakers, unless I want an actual fuzz sound in which case I use a germanium fuzz.

I think, for what treble boosters are logically intended to do in guitar rigs, the corrolary in a bass rig would be a full range boost, AKA clean boost pedal, and this would only make sense in front of a tube amp. Like, if I wanted some serious bass crunch from an amp with limited options, like a Vox AC50 or an old Fender bassman head, I might use one of those (although in the case of the AC50, I would first switch the preamp tube from a 12AU7 to a 12AX7 and that would probably do the trick).

teleharmonium is right, treble boosters are really for guitars. British amps tended to be darker than Fender amps. So the Brits used treble boosters to try to get the brighter "American" sound. Cheaper than trying to buy an import amp